DE filters and cartridge filters must be taken apart and cleaned as part of routine maintenance. DE filters once a year, and cartridge filters once every 6 months, or whenever the filter pressure goes up 10 pounds. Depending on the amount of dirt, debris or the bather load, etc, it may be necessary to clean a cartridge filter 3-4 times a year. You can backwash a DE filter, but residual build up of dirt, DE and debris, gets compacted between the grids and that can easily damage the grids. Opening the filter and cleaning and inspecting the grids must happen in addition to back washing throughout the year. Doing this maintenance can save you from unwanted problems and help save you money. Manifolds, air breather screens, cartridges and grids will last longer if they are kept clean and not allowed to get 'caked up' with debris.
Anytime you have a filter apart, you should be inspecting the filter components for damage. Shown below, are some worst case scenarios. More than likely, if there are cracks, or tears to the degree shown in the images below, you may already have a green pool, or a dirty pool. Dirt and water would be bypassing the filter and blowing back into the pool. The idea of routine cleanings and inspections, is to discover potential problems early. What you will be looking for is hairline cracks in the manifold, or the cartridge filters rubber, or tiny tears in the DE filter grid material. If you see any kind of wear, or damage in the early stages, this is the time to replace the damaged parts before it becomes a bigger problem.